How does one make a piece of writing "read like fiction," especially if it's a true story, say, of a kid getting stuck in a mailbox?

I’m looking through some writing competitions. One looks especially promising. It’s called Family Matters, a contest through Glimmer Train. It specifies, “We are looking for stories about families of all configurations.
It’s fine to draw heavily on real life experiences, but the work must read like fiction.

What, exactly, does that mean?